1. Field of the Invention
The invention relates to the field of surgical instruments and, more particularly, to a trocar assembly for piercing a wall of a body cavity.
2. Description of the Related Art
A trocar is a sharp pointed instrument used in surgical procedures where it is necessary to puncture the wall of a body cavity. Such a procedure is often performed in order to drain fluids from the body cavity using a cannula inserted in the opening. Trocars are also useful in performing endoscopic procedures. In such a procedure, a preliminary puncture is generally made with a cannula so that the body cavity can be inflated with a gas in order to lift the wall of the body cavity away from other organs which may lie beneath the wall. A standard trocar, disposed in a trocar tube, is then inserted into the body cavity through the first puncture. The trocar is then removed leaving the trocar tube in place and endoscopic instruments can then be inserted through the trocar tube.
Standard trocars are generally metal rods having a sharpened point, frequently of surgical steel. A commonly encountered problem associated with the use of trocar is that a significant risk exists that the trocar will pierce the wall of the body cavity and injure internal organs lying thereunder. Numerous disclosures have been made wherein this problem is addressed by disposing a spring biased shield over the trocar. The shield is pressed back or retracted when the instrument is pressed against a wall of a body cavity, thus exposing the piercing tip of the trocar. When the trocar has completely penetrated the wall, the shield is pushed forward to an extended position to shield the piercing tip of the trocar. Examples of patents dealing with this type of structure include U.S. Pat. No. 4,654,030 to Moll et al, U.S. Pat. No. 4,601,710 to Moll, and U.S. Pat. No. 4,535,773 to Yoon.
According to the prior art, the shield is a concentric sleeve which is disposed over the trocar and thus has a larger diameter than the trocar. Further, the trocar and shield are disposed for use in a trocar tube of still larger diameter. Thus, the piercing tip of the trocar is of the smallest diameter of all instruments which are to enter the cavity through the wall where it is pierced. In operation, such devices result in a stretching and tearing of the wound in order to accommodate the larger diameter of the shield and the further larger diameter of the trocar tube.
Further, the piercing tip cannot be shielded until the entire shield has entered the wound. Thus, such devices still allow a significant risk of injury to organs and other tissue lying beneath the wall to be pierced.
It is thus the principal object of the present invention to provide a trocar assembly having a shield which can be disposed for use with a minimum amount of stretching, and no tearing, of the wound made by the trocar.
It is a further object of the present invention to provide a trocar assembly having a shield which can more reliably and readily deploy to shield the piercing point of the trocar.
Other objects and advantages of the invention will become readily apparent to one skilled in the art upon a consideration of the following disclosure.